1. Field of the Invention
The present invention relates to an electroacoustic transducer, and more particularly relates to a small or miniature electrostastic loudspeaker (ESL).
2. Description of Related Art
Loudspeaker is an electroacoustic transducer for changing electrical signals into sound. The loudspeaker pushes a medium in accord with the pulsations of an electrical signal, thus causing sound waves to propagate to where they can then be received by the ear. According to the different physical effects of the electroacoustic conversion, the loudspeakers are divided into many kinds of types, such as magnetic loudspeaker, piezoelectric loudspeaker, electrostatic loudspeaker (condenser loudspeaker) and moving-coil loudspeaker (dynamic loudspeaker). Each type of the loudspeaker has advantages and disadvantages. In recent years, the moving-coil loudspeaker has been widely used because of the advantages in relatively great variety and mature manufacturing process.
The loudspeakers are almost applied in each kind of electrical consumer products. With the development of use in portable consumer products for audio communication and audio/video playing, such as walkman, cell phone, the market of the loudspeaker which is recognized as the key part of the consumer products becomes larger and larger.
At present, the moving-coil loudspeaker takes up a large share of the market. The moving-coil loudspeaker has a vibration system and magnetic system. The vibration system is operated by the electro-magnetic interaction to produce mechanical movement, and further radiate sound-waves into air. However, the vibration system has a heavy quality which limits the application of the moving-coil loudspeaker in the portable products. In addition, the frequency response is not flat and has worse performance in high-range frequency.
The electrostatic loudspeaker mainly has a diaphragm and stationary electrode which forms a capacitor with the diaphragm. The electrostatic loudspeaker is driven by the static-electricity on the capacitor to work. When the electrostatic loudspeaker works, the capacitor electrically connects with a pair of power sources to polarize the two electrodes, the diaphragm and stationary electrode, to produce an electrostatic field therebetween. When audio signals are inputted, the diaphragm is driven by the signal currents supplied by the electrostatic field to vibrate and sound, and then radiate sound-waves to exterior through sound apertures located on the stationary electrode.
The electrostatic loudspeaker adopts the static-driven vibration system which is light and thin without the coils and the like elements in the moving-coil loudspeaker. Therefore, the electrostatic loudspeaker can expand the high frequency characteristic, and meanwhile improve the flatness of the frequency response. The electrostatic loudspeaker also has an advantage of small distortion. Conclusively, the structure of the electrostatic loudspeaker is easy to be small-sized and light, and is in accordance with the development trend of electrical consumer products.